Is It Time To Celebrate America's Official Valuing Of Openness To Immigrant And Quota-Recruited Diversity RE: Scientific Publications?

We've been told for decades, and are still being told, that diversity strengthens and enriches us, and this may be expected to show in science and technology in particular.
Is there some reason why we may not look at the facts on this?
Below are the number of scientific publications per million population for the countries which are above the U.S. on this indicator of contribution to the advancement of civilization:
Sweden-1431
Denmark-1214
Finland-1157
Netherlands-963
U. K.-949
Belgium-810
Austria-717
U.S.-708 Germany 657, and France 652, are just below, but may have already moved beyond the American level in the last few years. From Scientific American April 2002, p.25
& for the individual year's data that the Scientific American averages were taken from see Cordis:
Scientific publications per million population
How could these countries, with so much less diversity, especially in their universities, have moved up to and soared beyond, the American level, if diversity strengthens and enriches?
If our diversity has increased from a point rather like these European countries today, why has it not allowed us to maintain our relative position to these countries, and how could it be associated with the opposite pattern, from that which was predicted, and still is predicted; that the more diversifying country should be relatively strengthening its contribution to advancement of civilization? Instead, we see the more diversifying countries being more and more surpassed, first by one, then another and another, less-diversifying country.
If any pro-diversity believers should be so bold as to answer the above, let them be forewarned that ad hoc excuse-making won't do at all.